> ## Documentation Index
> Fetch the complete documentation index at: https://mintlify.com/mermaid-js/mermaid/llms.txt
> Use this file to discover all available pages before exploring further.

# initialize()

Configures Mermaid with global settings that apply to all diagrams. This method should be called before rendering any diagrams with `run()` or `render()`.

## Signature

```typescript theme={null}
function initialize(config: MermaidConfig): void
```

## Parameters

<ParamField path="config" type="MermaidConfig" required>
  Configuration object containing settings for Mermaid rendering.

  Common configuration options:

  <Expandable title="properties">
    <ParamField path="theme" type="string">
      The theme to use for rendering. Options: `'default'`, `'dark'`, `'forest'`, `'neutral'`, `'base'`.
    </ParamField>

    <ParamField path="themeVariables" type="object">
      Override theme variables like colors and fonts.
    </ParamField>

    <ParamField path="fontFamily" type="string">
      Font family to use for all diagrams.
    </ParamField>

    <ParamField path="logLevel" type="string">
      Logging level. Options: `'debug'`, `'info'`, `'warn'`, `'error'`, `'fatal'`.
    </ParamField>

    <ParamField path="securityLevel" type="string">
      Security level for rendering. Options: `'strict'`, `'loose'`, `'sandbox'`.
    </ParamField>

    <ParamField path="startOnLoad" type="boolean">
      Whether to automatically render diagrams when the page loads.
    </ParamField>

    <ParamField path="maxTextSize" type="number">
      Maximum allowed text size for diagram definitions.
    </ParamField>

    <ParamField path="deterministicIds" type="boolean">
      Whether to use deterministic IDs for elements.
    </ParamField>

    <ParamField path="deterministicIDSeed" type="string">
      Seed for deterministic ID generation.
    </ParamField>
  </Expandable>
</ParamField>

## Return value

`void` - This method does not return a value.

## Examples

### Basic initialization

```javascript theme={null}
import mermaid from 'mermaid';

mermaid.initialize({
  theme: 'dark',
  logLevel: 'error',
  securityLevel: 'strict'
});
```

### Custom theme configuration

```javascript theme={null}
mermaid.initialize({
  theme: 'base',
  themeVariables: {
    primaryColor: '#ff6b6b',
    primaryTextColor: '#fff',
    primaryBorderColor: '#ff6b6b',
    lineColor: '#f5a442',
    secondaryColor: '#4ecdc4',
    tertiaryColor: '#ffe66d'
  },
  fontFamily: 'Arial, sans-serif'
});
```

### Configuration for automatic rendering

```javascript theme={null}
mermaid.initialize({
  startOnLoad: true,
  theme: 'default'
});

// Diagrams with class="mermaid" will be automatically rendered
```

### Deterministic IDs for testing

```javascript theme={null}
mermaid.initialize({
  deterministicIds: true,
  deterministicIDSeed: 'test-seed'
});
```

## Usage notes

* Call `initialize()` before using `run()` or `render()`
* Can be called multiple times to update configuration
* Configuration merges with existing settings
* When `theme` is specified, appropriate theme variables are automatically applied
* The `fontFamily` setting is propagated to `themeVariables.fontFamily` if not already set

## Related methods

* [run()](/api/methods/run) - Render all diagrams on the page
* [render()](/api/methods/render) - Render a single diagram to SVG